Help troubleshooting plz

[Cleveland180]

So here is the deal, I am at whits end with my car and it isn't getting any better. I cannot think of what else to do in order to get this bad boy running right so I was hoping I could get some help.

So far, I have changed the MAF, gotten a new O2 sensor, upgraded to a Walboro Fuel Pump, upgraded to a 300zx TT fuel filter, and checked my injector O-rings to make sure they were still healthy.

My problem is the car will start, but only runs at about 2000 rpm, the idle will not go down, and the engine will not rev. It simply stays in the 2.1-2.4k rpm range. I have a wide band hooked up, and at its insanely high idle the AFR is at 10.0 and when the gas pedal is pressed it bounces from 18.0 to 10.0 while the motor fails epically at running smoothly.

I previously had HKS spark plugs in the car, and changed them to NGKs IIRC, but there was no difference in engine behavior. Obviously the exhaust smells strongly of gasoline.

So what should I check next? I am really hoping to be able to drive the car soon, so any help finding this problem would be great. Thanks in advance! Dave

[SullivanRacing06]

motor? s chassis its in, who did your wiring, getting spark from all the coils?

[Cleveland180]

HA-HA ! Sorry, Its an rb20det, in a base s13 (1991), I did the wiring using the write ups online, and I am getting spark at all coils.

[eh?]

Check for codes and check your maf wiring.

[Cleveland180]

I will try to check the codes. But I know the maf wiring is right, signal at the rpm I was stuck at is 34xx mV or something like that.

Another thing I just thought of, before I got the exhaust and intercooler piping routed I was able to free rev the engine, but that was a year ago and it hasn't done that since, idle has always been high though.

[Cjmartz2k]

Big a** vacuum leak. Make a boost leak checker.

[Cleveland180]

Could it really be something that simple? am not saying it's impossible, but at my idle i am at 18-19 psi vac.

Sadly I live two hours away from my car, and only get to work on it once every two weeks, so I am hoping to get a check list of things I can do so that I don't waste my time searching for symptoms, and ripping my car apart, when I could at least do tests to narrow things down.

So far:Check CodesDouble Check Spark/coilsBoost Leak CheckClean IAC, adjust Idle screw

[nos487]

Try to pinch off air regulator hose. Mine was not wired in and air regulator was stuck open.

[Cjmartz2k]

Real easy to check a boost leak so it's worth eliminating. BTW, what part of Cleveland are you from? I used to live over off Fleet Ave.

[Cleveland180]

I am over off rocky river drive, and puritas. But most of the time i am at school in Toledo. If you could give me a hand sometime I would really appreciate it. usually work on my car every other weekend.

[Cjmartz2k]

O yeah, over by Maley's just off 480. I know the area. I live in NC now though so if might be tough to help wrenching.

Give making a boost leak checker a shot. All things being equal, the simplest answer is usually the correct one. Might not be it, but it's pretty easy to check.

[Cleveland180]

Yeah that would make it a little inconvenient haha, I will give the boost leak check a go, I still have one i made for my SRT-4 so I am hoping I can find a spot to hook it up. Thanks, Dave

[RustspecS13]

Yeah check for a boost leak. Maybe try to put the maf right off the J pipe/throttle body to eliminate all the stock piping if you can't build a boost leak tester.

That seems pretty likely, since its a fresh swap the couplers could be bad.

Thoroughly check those and let us know how that goes.

~Alex

[Cleveland180]

Well I made the trek home to work on my car some this weekend and here is what I got.I pulled the codes and I got Maf circuita/t controlTPS circuit

So, I pulled the IACV and AACV and cleaned them up, then adjusted the idle, and replaced the gaskets. I also removed the TPS to see if anything on there needed to be clean, but all the contacts looked nice and clean, and everything moved smoothly. I started up my engine with all the sensors pugged in, and it ran exactly the same, I unplugged the sensors one by one, and each produced an audible change in the way the engine ran. I assume they are working.As for the maf wiring, I checked my wiring and I am hoping for some conformation on my wiring.blk/wht = powerblack= groundother black= signal ground white= sensor feedback. I do have a Turbo XS d-tec wired in and I can see that my maf load is at 3.5V when it is running at the crappy idle. The D-tec also draws from the TPS and that does not seem to be working. I assume the the tps would still send a signal when the key is turned but the engine is off, however the signal is not changing when i open and close the throttle. But, like I said, when the tps is unplugged the engine is definitely affected. I also did a boost leak test and found that two small caps I had put on cracked and were leaking, so I replugged them, but they didn't fix anything. I tested my fpr's and they are both working. I read in another topic that our cars are very picky when it comes to any oddities in the signals, so I made sure that all my solders were good, and they are. Any Ideas? I am currently thinking about buying another motor set, and just switching everything over, but I really don't wanna do that since it's a rb20 and i feel like it would be a shame for me to be hogging all of them, not to mention that would be another $1300 on an engine and times are tough in this great country.Any help would be appreciated.

[Cleveland180]

New info, My maf is sending a 3.1V signal before I even start the car, should it be at 0V when there is no load?

Thanks

[RustspecS13]

Sounds like the maf is bad or wired wrong, I don't for sure if it should be zero, but but it should be in the .5 to 1v range at an idle. 3V is completely wrong.

~Alex

[WhatsADSM]

Yea those MAF readings are pretty wacked.

check the wiring/maf

[Cleveland180]

I thought it seemed a little weird, it has done the same thing for both maf's I have used so I guess my wiring must be messed up. I didn't think that it was all that confusing from all the diagrams available out there, but I guess I was wrong. I will do work on it this weekend and let you guys know what happens. Does anybody know if we can use any USDM TPS's ? I was google-ing the crap out of our part number and just kept coming back with garbage...

[Carl H]

maf wiring is wrong.sheilded black wire on the rb20det harness is signal while white is the ground.

[Cleveland180]

ok, well I am working on my car today, and I have switched wires around, but with no luck. I had it so that the maf signal was at .5V before the engine was started, but it refused to start without starting fluid, after the starting fluid ran out, it would just die. I also had it so the maf signal was in the single digit millivolt range, and that seemed to do nothing to correct my issues. When I did get my maf in the .5V range all my codes went away and the ecu was giving me the good ol' 55 (all clear), Any ideas what is going on?I do have fresh 93 octane in the tank, fuel pump is priming well, I am assuming the spark plugs are good, because when my signal is 5v or 3.5v the car will start right up. but the idle is garbage. So clueless what to do next.

[Carl H]

may have fried the maf or the ecu maf grounding circuit.

[Cleveland180]

I threw the N60 back on and had the same results, I am going to open up the ecu and look for burn marks now.

[Cleveland180]

I opened up the ecu and searched for anything out of the ordinary, all the connections are clean, and there is not even a single resistor that is darkened or burnt up. I unplugged the MAF all together and the car starts right up, idles at 2000 and will not budge from there. If I plug the MAF in, the signal drops from ~5V down to 0.5V and dies immediatly... What are my options for fixing this? It is finally done snowing up here and if I dont get to drive this car soon, I may not get the chance for a long while.

[Yellow4g63]

I opened up the ecu and searched for anything out of the ordinary, all the connections are clean, and there is not even a single resistor that is darkened or burnt up. I unplugged the MAF all together and the car starts right up, idles at 2000 and will not budge from there. If I plug the MAF in, the signal drops from ~5V down to 0.5V and dies immediatly... What are my options for fixing this? It is finally done snowing up here and if I dont get to drive this car soon, I may not get the chance for a long while.

double check your wiring with the volt meter make sure you wired up the maf right. check for vacuum leaks sounds like your almost there.

[Carl H]

if the maf voltage isnt changing when you rev the engine sounds like the maf has packed up and gone.

[Cleveland180]

I can't even get the engine to stay on with a MAF plugged in. This are the situations I have come across.When it is stuck at 3V with maf wired wrong the engine will start and but will not allow any throttle.When the maf is wired correctly the engine will not start. (0.5V with the key in the on position)With the maf unplugged the car will start and behaves the same as if the MAF is wired wrong (3V style)

[Carl H]

perhaps still a wiring issue?electrical is super hard to diagnose...hence why i charge out the arse to do it.

[Cleveland180]

Yeah it sure is... And I understand why you charge for your services... sadly I have worked on my harness too much to send it out, without being cursed by whoever I would send it to. I dont know what is going on with this car, sometimes I wonder if it will ever run correctly

[Carl H]

did you check under the ecu, not just top side for a burned trace?been my experience that there is normally a burned trace on the bottom of the ecu but topside almost nothing

[Cleveland180]

well I opened up the bottom of the ecu to check, and there was nothing, no odor, no burns, nothing. I unplugged my IACV and my tps and the car actually runs and idles better without them, but is still in limp mode. I am considering a new ECU without any tune, and also a z32 maf... My current ecu has a veilside tune and it could be for a car with bigger injectors or something..